A current trend in lighting is that light is more and more used for creating an atmosphere rather than for just illumination. Lighting systems suitable as “atmosphere providers” need to be capable of emitting light of different colors as well as being variable in intensity (dimmable). Ideally, such lighting systems should be variable over the entire color triangle (for example in the xy-plane of the CIE XYZ-system) perceptible by a human eye. In reality, however, a color variable lighting system can span only a part of the color triangle. For a particular color variable lighting system, this part of the color triangle is referred to as the color gamut of the lighting system. Moreover, different lighting systems generally have different color gamuts.
U.S. Pat. No. 5,384,519 discloses an example of such a variable color lighting system in which light from at least three dimmable mono-color light sources is mixed in order to emit light of a desired color. When the different LEDs are far apart in color space (as is the case with RGB), making colors in the centre of the range (whites) is relatively simple and the possible range and flux is relatively independent of the exact position of the primaries. However, a disadvantage of such a system is the sensitivity of color point in relation to color temperature and a rather limited color rendering index (CRI).
Since the color gamut of any variable color lighting system only spans a part of the color triangle, there is always a possibility that a user may request light of a color outside the color gamut of the lighting system. As the light sources in a color system may be slightly different between one system and the next due to uncontrollable variations in the fabrication process, two apparently similar lighting systems may provide slightly different color gamuts. The uncertainty in which color can be provided be the lighting system can for example be eliminated by limiting the allowable gamut of the modules to the minimal gamut that can always be guaranteed. However, such a limitation would be excessive in most cases.
Furthermore, there are known solutions for approximating a color point within an allowable gamut if a requested color lies outside of the allowable gamut. However, merely approximating a new color point within the allowable gamut, for example the nearest point within the gamut, may provide a color which is perceived as significantly different from the requested color with respect to color temperature and CRI.